Hydrogels are primarily composed of synthetic or natural hydrophilic polymers. Owing to their 3-D structures, which resemble that of extracellular matrices (ECMs), hydrogels have been employed as tissue substitutes, space-filling scaffolds, and cell carriers. To achieve maximal benefit, the hydrogel composition must be compatible with the mechanical (for example, modulus), physical (for example, mass transport) and biological (for example, cell-matrix interaction) requirements of each biomedical application under consideration. In particular, injectable hydrogels as biomaterials are attractive for many biomedical applications.
Strength of hydrogels depends largely on their cross-link density, which may be physical (reversible) or chemical (permanent) in nature. Physical networks may be present in hydrogels such as collagen, chitosan, and aminated hyaluronic acid (HA)-g-poly(N-isopropylacrylamide), whereas chemical networks may be found in chitosan-HA, polyethylene glycol-fibrinogen, and alginate hydrogels. However, such systems are usually weak isotropic materials and are not able to bear significant loads, such as those presented by living tissues, and also suffer from poor stability and survival following engraftment.
Fiber reinforcement may be used to strengthen hydrogels and to obtain composite structures featuring anisotropic mechanical behavior. Supportive impact of hydrogel/electrospun fiber composites on cell growth and differentiation has been reported. However, incorporation of fibers and their proper dispersion within the host material still pose a technological challenge, especially in case of injectable hydrogels, where injectability is required and blockage of needles must be avoided.
In view of the above, there remains a need for hydrogel compositions, and methods of forming the hydrogel compositions that address at least one of the above-mentioned problems.